Shogun is a 1.5 years old black and tan male shiba. He is known as a super friendly dog, he never got into a fight even if the other dog was hostile towards him. He would avoid fighting. If he approached a dog or meet a dog or dogs outside during our daily walk and that dog is hostile, growling or even picking up a fight, sho would just turn away and walk away with me. If the dog keeps on picking on him ,he would only show his teeth without any growling sound and close his mouth as fast as he opens it just to tell the other dogs to stop picking on him.

Today when me and sho was walking, a guy and a lady with 3 dogs passed by. One is a labrador, one is a kooka, and the other one is a poodle. These 3 dogs was immediately hostile when they see sho, so i dragged sho behind me with the leash so i can protect him. But as it turns out, the 3 dogs still charges forward, and as fast as lightning, instead of me protecting sho, it became sho protecting me, sho dashed from behind me and in a blink of an eye he is already in front of me and attacking the kooka, biting it on its face and i can see the skin on that poor dog's face is torn apart. The other 2 dogs did not intervene, they just stand still like a statue, i guess they are shocked to see how fast and furious sho is that they decided not to charge and attack sho anymore.
The guy and the lady quickly dragged their dogs away and ending with me and them yelling at each other. The lady was about to come back when she sees sho limping on his front leg, i guess she doesn't want trouble and immediately left. I checked sho's front leg but no bite marks was on it, i checked his face and everything and not a single bite mark was on him. When they left, suddenly sho was cured from his 'limping' and walk calmly like nothing ever happened.
This incident really surprises me. Because sho NEVER was a bully dog or a hostile dog!
I don't understand what is happening just now? Is it because he is growing up to be a teen now and i should be more careful when i walk and meet other hostile dog? Or did he just try to protect me?
Anyone has any idea or has the same experience with me before? Where your dog never is hostile towards others then suddenly tear other dogs apart?
Thank you so much for the answer!

As dogs turn from puppy to adult, they will show less tolerance to strange dogs especially if their experiences aren't always positive ones. You may want to consider consulting a behaviorist, not only to help you learn Sho's threshold but to also get advice on how to deal with hostile dogs.

At the very least, carry a stick or something to protect the two of you during walks. Pissing people off by whacking their dogs with a stick is better than risking Sho's life or causing major injury to either dog.

I'm glad I live in the countryish only got to deal with one snarly rat terrier it's more bark then bite so far I just stay away from her.

On walks if the dog is acting mean or too excited I'd avoid walking near them don't want them to come after you.

It's kinda the three dog owner's fault if their dog is not friendly or too excited they should have kept control of their dog..

I'd never let my dog meet a strange dog I don't know or if they get too mean.

Saya is leash reactive she doesn't greet strange dogs too well on leash off she is good so I never let her meet strange dogs.

Took Saya three or four visits to greet lily my cousin's pug took a walk with her and she was great with lily, but before she'd get mad if lily came near.

Glad Sho is OK only dog issues I've had was off leash dogs my last boxer Pearly was attacked by a big chow chow that was poorly socialized and bolted out of the house thankfully She wasn't hurt.
Nicole, 5year old Bella(Boxer), and 4year old Saya(Shiba inu)

A colleague of mine also has a Shiba and we got them together today. We immediately went in a walk and this is what happened.

Never in his life have I seen Oki be anything other than playful to another dog but he took an instant dislike to my friends' Shiba. There was a lot of growling and snarling between them. We went for a walk and they seemed fine towards the end then we let them off in the garden (Oki's garden) and there was a lot of sniffing and Oki went from tense to playful. The other dog did not appreciate the attention and did give him a warning growl but stupid Oki ignored it and carried on trying to get him to play. The other dog then flew round and a fight ensued. After they calmed down they were fine again, and Oki ignored the other dog. However, now the tables were turned abd the other dog was incessantly sniffing Oki, mostly his willy...and Oki turned his head away etc but the other dog carried on. Seems they both have no manners and both had backing down issues! They are both intact males, Oki 7 months and the other 18 months. Oki is totally fine with all the dogs in all his training classes so not sure why the severe dislike today. They met very briefly before once and the other dog was quite growly and Oki was placid that time. Sorry about the long post, sad my little man has it in him to appear so aggressive! He's shattered now bless him.

I know they can't like every dog they see. Oki has never reacted this way before. We spent a weekend with friends and their dog no problem, and he's now fine with my mums dog (though that was never nastiness, just Oki being a bit of a rude playful puppy). I suppose it coukd be number of factors, maybe the start of the walk was too close to his territory? Maybe them being 2 intact males fidn't help? There's such a variety of intact and "done" dogs at all his training classes, he's never had a problem before.

There is a big difference between Oki walking next to another leashed dog on neutral territory, and having another dog in Oki's backyard and personal territory. My guess is they needed a few more walks to get comfortable with each other, and possibly doing the first off leash playtime in a neutral fenced area not "owned" by either dog.

Some dogs would be fine after just one walk for an introduction, but these two started off not liking each other, so it will take more work to make them tolerate each other, especially if one dog is on home turf.

Not all dogs will become friends, just like not all people will become friends.

Since both dogs are still working on their social skills, it might be a good idea to watch them and help out when one is getting tense by distracting the pestering dog. I wouldn't use treats or toys though, because one or both dogs may become possessive.

I have friends that have half sibling pups who are close in age (same sire.) They visit each other often and the dogs play great together usually, but when one gets tired/grumpy we have to distract the higher energy dog to prevent a scuffle. I usually do this by taking the spunkier pup for a brisk walk, or play tag with him/her until the other pup decides to join back in. They have known each other since they were pups, and are very happy when they get to see one another, but they can still squabble and need supervision.

Don't take this the wrong way but. I think you and the other owner need to step up your game a bit. Since you observe the situation and SAW that the other dog was not liking what Oki is doing, and clearly Oki did not take the growling as a sign to back off, you should have stepped in. Something simply like "Oki Come" would suffice, and if that was not enough, distract him with something better. @RustyAngel had some nice suggestions, occupy and tire out Oki until the other Shiba is ready to join in.

We did distract them at regular intervals by calling them and talking to them etc. They'd just go straight back and bother each other. The incident happened just as we were thinking we'd better separate them in order to leave it on a good note. (My friend suggested distracting them with some new tennis balls she brought but I thought even thought she had several that might just lead to a fight over possesions. Especially as her dog has known guarding issues). After the scrap, they calmed down and we let them interact again so as not to leave things on a bad note. Like I said, the other dog started licking him a lot "down there" (what does that mean?!) and Oki wasn't massively pleased but didn't react so other dog was pulled away and off he went. Once the dog had gone Oki ran around the house (even though they were never in the house) for a minute seemingly looking for the other dog. I guess to just check he was truely gone? He settled down really quickly though.

I agree, thinking back it was not a good move to have the other dog in our garden, but there are no secure neutral areas. Dog parks and similar secure, fenced areas simply don't exist here. If we ever meet up again we will just go for a walk and that be that.

Towards the end it was my friends Shiba that was doing most of the pestering. I've definitely learnt from this. It's not something I've ever seen / had to deal with before so next time it will be dealt with quicker now I'll be able to recognise the warning signs quicker.

Never seen this behaviour from Oki. Was upsetting. However, I was told this is the norm for her Shiba as she admits not socialising him much as he got kicked out of puppy class for being aggressive. I'm sure I'll put Oki through meeting again to be honest.

On the plus side, he seems completely unphased by it all as we went to training as normally the same evening and he was absolutely fine. Wanted to say hello to every dog as usual and was acting playful.

based on your story it sounds like Sho was protecting you - Fen gets in front of me when strange dogs try to come up to me. I think it's funny that Sho was acting hurt - I have seen Fen do that too. I'm glad you were both OK! I understand your surprise at Sho's viciousness - I felt the same way first time I saw Fen get really mean. They are so tiny and cute and then WHAM . . . some dog is bleeding and your Shiba isn't even out of breath.